JPH0566164A - Magnet-striction type torque sensor - Google Patents

Abstract

PURPOSE:To detect torque applied to a magnet-striction shaft with high accuracy from a pulse duty ratio in a magnet-striction type torque sensor by using a multivibrator circuit as a detection circuit. CONSTITUTION:An oscillating circuit 21 is formed in which the rise time and fall time of pulses are varied with changes in the self inductances L1, L2 of detecting coils 7, 8 each of which detects torque applied to a magnet-striction shaft. Since the oscillating circuit 21 is such that the self inductance L2 is decreased as the self inductance L1 increases, the pulse duty ratio is varied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetostrictive torque sensor which is preferably used for detecting torque generated in an output shaft of an automobile engine.

[0002]

2. Description of the Related Art Generally, in an automatic vehicle or the like having an automatic transmission mechanism, it has been proposed to attach a torque sensor to a propeller shaft or the like in order to optimize the shift timing by the automatic transmission mechanism.

As such a torque sensor, a conventional torque sensor shown in FIG.
And the magnetostrictive torque sensor shown in FIG. 5 is known.

In the figure, reference numeral 1 denotes a magnetostrictive shaft made of a magnetostrictive material such as chrome molybdenum steel. The magnetostrictive shaft 1 is provided, for example, in the middle of a propeller shaft. The side mounting portion 1B becomes the slit forming portion 1C in the middle thereof, and the slit forming portion 1C has an outer periphery of 45 ° downward and 4 ° upward.
Slits 2 and 3 engraved at 5 ° are provided so as to face each other.

Reference numeral 4 denotes a coil fixing member provided so as to be rotatable relative to the magnetostrictive shaft 1 via a pair of bearings 5 and 5 so as to surround the outer periphery of the slit forming portion 1C. It is fixedly attached to the vehicle body. Reference numeral 6 denotes a ring-shaped core member fixed to the inner peripheral side of the coil fixing member 4. The core member 6 is provided with detection coils 7 and 8 at positions facing the slits 2 and 3, respectively. The self-inductance of the coils 7 and 8 are L1 and L2.

FIG. 5 shows a detection circuit, which is composed of a bridge circuit 9, an oscillator 10, a differential amplifier 11, a synchronous detection processing circuit 12, a display 13 and the like.

Here, the bridge circuit 9 includes the detection coil 7,
8, iron loss r1 and r2 of the detection coils 7 and 8 and adjusting resistance
It is connected as shown in FIG. 5 by R and R, and between the connection points a and b
Connected to the oscillator 10 of voltage V and frequency f (for example, 30KHz)
And the connection points c and d are the output voltage V of the detection coils 7 and 8.
It becomes an output terminal for deriving 1, V2, and the connection points c, d
Are respectively connected to the input terminals of the differential amplifier 11.
It Output voltage E from the output terminal 14 of the differential amplifier 11
0 is the alternating current of the oscillator 10 on the input side of the synchronous detection processing circuit 12.
Input together with the voltage V, and the synchronous detection processing circuit 12 outputs
Voltage E Synchronize 0 with AC voltage V to rectify DC power
The pressure E is converted and output to the display 13. In addition, each adjustment resistance
Anti-R is output when the torque acting on the magnetostrictive shaft 1 is zero.
Voltage E Balance the bridge circuit 9 so that 0 becomes zero
Adjusted to the state.

In the two-coil type magnetostrictive torque sensor constructed as described above, the oscillator 1 is connected to the detection coils 7 and 8.
When an AC voltage V of 0 is applied, a magnetic path is formed on the surface of the magnetostrictive shaft 1, but since the slits 2 and 3 are provided on the surface of the slit forming portion 1C, the magnetic path due to the surface magnetic field is the slit 2. 3 is formed.

On the other hand, the input side mounting portion 1A of the magnetostrictive shaft 1
When a torque T in the direction of the arrow as shown in FIG. 4 is applied to the slit 2, a tensile stress + σ is generated in the slit 2 and a compressive stress −σ is generated in the slit 3. When a positive magnetostrictive material is used for the magnetostrictive shaft 1, the tensile stress + σ
Increases the magnetic permeability μ, and the compressive stress −σ increases the magnetic permeability μ.
Is known to decrease.

Therefore, the self-inductances L1 and L2 of the detection coils 7 and 8 are calculated by the following formula 1.

[0011]

[Equation 1]

In the bridge circuit 9, L1, r
Since 1 is connected to R and L2 and r2 are connected to R in series, the currents i1 and i2 flowing through the detection coils 7 and 8 are expressed by the following formula 2.

[0013]

[Equation 2]

The output voltages V1 and V at the connection points c and d
2 becomes like the following formula 3.

[0015]

[Equation 3] Where α1, α2: phase angle

Further, the output voltage E0 output from the output terminal 14 of the differential amplifier 11 is given by the equation (4).

[0017]

[Equation 4] E0 = A × (V1−V2) where A: amplification factor

In the synchronous detection processing circuit 12, the output voltage E0 from the differential amplifier 11 is synchronously detected and rectified by the AC voltage V from the oscillator 10, and the torque T acting on the magnetostrictive shaft 1 is converted into the DC voltage E. As display 13
The torque T is displayed as a DC voltage E on the display 13.

Thus, the magnetostrictive shaft 1 is moved in the direction of the arrow.
When Luk T is added, tensile stress + σ on the slit 2 side
Since the magnetic permeability μ increases due to the
The self-inductance L1 of the detection coil 7 increases,
The current i1 flowing through the detection coil 7 decreases and the output voltage V
1 decreases. On the other hand, on the slit 3 side, the compressive stress becomes −σ.
Since the magnetic permeability μ is further reduced, it faces the slit 3.
The self-inductance L2 of the detection coil 8 decreases,
The current i2 flowing through the detection coil 8 increases and the output voltage V2
Will increase. The output voltages V1 and V2 are calculated by
1 and the phase difference α1
 , Α2 is generated and the amplitude is
Change (voltage value). In particular, this phase difference
Output voltage E according to equation 4 0 is a relatively large amplitude (voltage value)
And the detection signal proportional to the torque T in the direction of the arrow
Output voltage E It is output to the synchronous detection processing circuit 12 as 0, and
Display the negative DC voltage E corresponding to the torque T on the indicator 13.
It

On the other hand, the electromagnetic shaft 1 has a direction opposite to the direction of the arrow.
When the torque T of is applied,
The flow i1 increases and the current i2 flowing through the detection coil 8 decreases.
From the output voltage E Synchronous detection processing as 0
Output to the logic circuit 12 and correspond to the torque T on the display 13.
Display the positive DC voltage E.

[0021]

By the way, in the above-mentioned prior art, the stress generated in the magnetostrictive shaft 1 is detected as a change in the self-inductances L1 and L2 of the detection coils 7 and 8, and the bridge circuit 9, the oscillator 10 and the differential circuit are detected. Motion amplifier 1
1, the synchronous detection processing circuit 12, the display 13 and the like are processed by the detection circuit, so that the circuit configuration of the detection circuit becomes complicated and the oscillator 10 and the synchronous detection processing circuit 12 have high accuracy. Since a circuit is required, there is a problem that the cost becomes high.

The present invention has been made in view of the above-mentioned problems of the prior art. The present invention has a magnetostrictive torque sensor which can improve detection accuracy as well as cost reduction by configuring a detection circuit with a simple electronic circuit. Is intended to provide.

[0023]

The features of the configuration adopted by the present invention to solve the above-mentioned problems are that the detection circuit is constituted by a multivibrator type oscillation circuit that oscillates by the inductance of each detection coil. The torque is calculated from the pulse duty ratio based on the signal from the oscillator circuit.

[0024]

With the above structure, the change in the torque applied to the magnetostrictive shaft is detected as the inductance of each detection coil, and the change in the inductance makes the rise time and fall time of the pulse generated from the multivibrator type oscillation circuit variable. Thus, the pulse duty ratio can be changed.

[0025]

Embodiments of the present invention will be described below with reference to FIGS. In the embodiments, the same components as those of the above-described conventional technique are designated by the same reference numerals, and the description thereof will be omitted.

FIG. 1 shows a detection circuit, which is roughly composed of an oscillation circuit 21, a waveform shaping circuit 29, a smoothing circuit 35, and an amplification circuit 38 which will be described later.

Reference numeral 21 denotes an oscillating circuit. The oscillating circuit 21 is composed of a collector-coupled astable multivibrator circuit, and a switching transistor 22 connected in series with a detection coil 7 between a reference voltage Vcc and ground and the switching circuit 22. Facing the transistor 22, the reference voltage Vcc
And a ground connected to the switching transistor 23 connected in series with the detection coil 8 and a connection point between the detection coil 7 and the switching transistor 22 and the base of the switching transistor 23 to set a time constant. A base resistor 24 having a resistance value R1 is connected in parallel between the connection point between the detection coil 8 and the switching transistor 23 and the base of the switching transistor 22 so as to face the base resistor 24. The base resistor 25 has a resistance value R2 (= R1) for setting a constant. Also, 26,
Reference numeral 26 is a current adjusting resistor connected in series with the Zener diodes 27, 27 between the connection point between the output side of the detection coils 7, 8 and the switching transistors 22, 23 and the ground, and 28, 28 are the above-mentioned. Base resistance 24,
25 is a speed-up capacitor that is connected in parallel to 25 and reduces the time constant of the switching transistors 22 and 23. The transistors 22 and 23 use the same transistor.

Further, the oscillation circuit 21 includes the self-inductances L1 and L2 of the detection coils 7 and 8 and the base resistance 24,
The switching transistors 22 and 23 are alternately turned on by the time constant set from the resistance values R1 and R2 of 25, and the square wave output voltage V1 from the connection point A between the Zener diode 27 and the resistor 26 on the switching transistor 23 side. Is output to the waveform shaping circuit 29.

The peak value of the square wave of the output voltage V1 approaches the reference voltage Vcc, the rise time of the output is the ON time (TON1) of the transistor 22, and the fall time is the ON time (TON2) of the transistor 23. Become.

Here, TON1 of the transistor 22 is expressed by the following formula 5.

[0031]

[Equation 5] However, V02: Voltage loss of the detection coil 8 hie1: Input resistance of the transistor 22 hfe: DC amplification factor of the transistor 22

TON2 of the transistor 23 is given by the following equation 6.

[0033]

[Equation 6] However, V01: voltage loss of the detection coil 7 hie1: input resistance of the transistor 23 hfe: DC amplification factor of the transistor 23

According to these equations 5 and 6, the oscillation frequency f
Is

[0035]

[Equation 7] And the pulse duty ratio D1 is

[0036]

[Equation 8] Becomes

Reference numeral 29 denotes a waveform shaping circuit. The waveform shaping circuit 29 is composed of a hysteresis comparator circuit, is connected in series between the operational amplifier 30, the reference voltage Vcc and the ground, and is connected to the non-inverting terminal of the operational amplifier 30. The resistors 31 and 32 for setting the input judgment voltage Vi and the resistors 31 and 32 connected to the output terminal of the operational amplifier 30
A feedback resistor 33, 34 connected to each input side of 32, and the inverting terminal of the operational amplifier 30 is the oscillation circuit 2
It is connected to a connection point A between the Zener diode 27 and the resistor 26 on the side of the switching transistor 23 where the output voltage V1 of 1 is output. Then, in order to shape the square wave of the output voltage V1 from the oscillation circuit 21 into a perfect square wave, the feedback resistors 33 and 34 are applied to the input voltage equal to or lower than the judgment voltage Vi.
The shaping voltage V2 having the peak value set by is output. In addition, in this rectification, while setting the peak value again,
Since the rising time TON1 and the falling time TON2 are inverted and output, the pulse duty ratio D of the shaping voltage V2 output to the smoothing circuit 35 is

[0038]

[Equation 9] Becomes

Reference numeral 35 represents a smoothing circuit. The smoothing circuit 35 constitutes an L-type integrating circuit by connecting a resistor 36 and a capacitor 37 in an L-shape to smooth the shaping voltage V2 from the waveform shaping circuit 29. Convert to DC voltage E1.

Reference numeral 38 denotes an amplifier circuit, which is composed of an operational amplifier 39, amplifies the DC voltage E1 from the smoothing circuit 35, and outputs it to a display or the like.

The magnetostrictive torque sensor according to the present embodiment has the above-mentioned structure. Next, the operation of detecting the torque applied to the magnetostrictive shaft 1 will be described with reference to FIGS. 2 and 3.

FIG. 2 shows the shaping voltage V2 from the waveform shaping circuit 29. When torque is not applied to the magnetostrictive shaft 1, torque is applied to the magnetostrictive shaft 1 in the direction of the arrow in FIG. 4) is applied to the magnetostrictive shaft 1 in the opposite direction of the arrow in FIG. 4 (hereinafter referred to as “negative direction torque”).

Here, when torque is not applied to the magnetostrictive shaft 1, the pulse duty ratio D1 (that is, the pulse duty ratio D) of the above equation 8 becomes 50% by adjusting the base resistors 24 and 25. Is set.

Next, when a torque in the positive direction is applied to the magnetostrictive shaft 1, as described in the prior art, on the slit 2 side engraved in the magnetostrictive shaft 1, the magnetic permeability μ is increased by the tensile stress + σ. It increases and the self-inductance L1 of the detection coil 7 facing the slit 2 increases, while the permeability μ decreases on the slit 3 side due to the compressive stress −σ, and the self-inductance L2 of the detection coil 8 facing the slit 3 increases. Is reduced. As a result, the relationship between the rising time TON1 and the falling time TON2 of the output voltage V1 output from the oscillator circuit 21 can be calculated from the above equations (5) and (6).
It becomes TON2. Further, the output voltage V1 is applied to the waveform shaping circuit 2
Since it is inverted by 9, TON1> TON2, and the waveform is as shown in the middle part of FIG.

On the other hand, when a negative torque is applied to the magnetostrictive shaft 1, a pulse waveform of TON1> TON2 is output at the output voltage V1 output from the oscillation circuit 21, and the waveform shaping circuit 29 causes TON1 <TON2, and the waveform is as shown in the lower part of FIG.

Next, the pulse duty change rate α when torque is applied to the magnetostrictive shaft 1 will be described. The pulse duty change rate α indicates the change rate α based on the pulse duty ratio D0 when the torque is zero, and can be calculated as in the following Expression 10.

[0047]

[Equation 10]

Since the pulse duty change rate α corresponds to the change in the DC voltage E1 from the smoothing circuit 35, a linear characteristic is obtained with the voltage value of the DC voltage E1 when the torque application is zero as a reference. And the amplifier circuit 3
As shown in FIG. 3, a DC voltage E proportional to the magnitude of the torque is output from the No. 8.

Thus, according to this embodiment, the oscillation circuit 21 is constituted by the multivibrator circuit in which the detection coils 7 and 8 for detecting the torque applied to the magnetostrictive shaft 1 are part of the circuit configuration, and the oscillation circuit 21 Output voltage V1
By connecting the waveform shaping circuit 29, the smoothing circuit 35, etc. to the, the pulse duty ratio D of the shaping voltage V2 from the waveform shaping circuit 29 is changed by the torque applied to the magnetostrictive shaft 1, and the pulse duty ratio D is changed. , The torque is detected as the DC voltage E, and highly accurate torque detection can be performed.

Further, as in the prior art, the bridge circuit 9,
It is not necessary to provide circuits such as the oscillator 10, the differential amplifier 11, the synchronous detection processing circuit 12 and the like outside, and the circuit configuration can be simplified and the cost can be reduced.

In the above embodiment, the pulse duty ratio D when the torque applied to the magnetostrictive shaft 1 is zero is 50%.
However, if the amplifier circuit 38 is used by arbitrarily setting the amplification factor with respect to the pulse duty ratio D when the torque is zero, the initial setting in the oscillation circuit 21 can be omitted. can do.

Although the oscillator circuit 21 is composed of the transistors 22 and 23 and the like, it may be composed of an IC of a logic circuit.

Furthermore, although the two-coil type torque sensor has been described in the above embodiment, the present invention is not limited to this, and it is not limited to this.
It can also be used for a coil type torque sensor.

[0054]

As described above in detail, according to the present invention, the detection circuit is constituted by the multivibrator type oscillation circuit in which each detection coil for detecting the torque applied to the magnetostrictive shaft is part of the circuit configuration. Torque can be calculated with high accuracy with a simple circuit configuration from the pulse duty ratio based on the signal from the oscillation circuit, and the cost of the detection circuit can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a detection circuit of a magnetostrictive torque sensor according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between torque and pulse output when torque is applied.

FIG. 3 is a characteristic diagram showing a relationship between torque and DC voltage obtained in the example.

FIG. 4 is a configuration diagram of a magnetostrictive torque sensor according to a conventional technique.

FIG. 5 is a circuit configuration diagram of a detection circuit according to a conventional technique.

[Explanation of symbols]

 1 Magnetostrictive shaft 7, 8 Detection coil 21 Oscillation circuit 29 Waveform shaping circuit 35 Smoothing circuit 38 Amplification circuit L1, L2 Self-inductance D1, D Pulse duty ratio α Pulse duty change rate

Claims (1)

[Claims] 1. A magnetostrictive shaft, at least a pair of detection coils provided on the outer peripheral side of the magnetostrictive shaft, and a detection circuit for calculating a torque applied to the magnetostrictive shaft by a change in inductance from each detection coil. In the magnetostrictive torque sensor, the detection circuit is composed of a multivibrator type oscillation circuit that oscillates by the inductance of each detection coil, and the torque is calculated from the pulse duty ratio based on the signal from the oscillation circuit. A magnetostrictive torque sensor characterized by the above.